Process for infusing high levels of humectant into dried fruits, for use in dry foods, such as in mixes and ready to eat cereals

ABSTRACT

The invention relates to the preparation of fruit for use in packaged dry foods, such as mixes and ready to eat ceral. A method of infusing high levels of liquid humectant into fruits such as raisins, without generating a stream of waste humectant, is disclosed. The method comprises applying a relatively high level of liquid humectant as a surface coating, and allowing the raisins to stand for enough time for most of the humectant to be absorbed into the fruit, before admixing the resulting fruit the dry food for packaging. 
     For dry foods having very low Water Activity levels, e.g. 0.30 and below, special means are disclosed for increasing the liquid humectant carrying capacity of the fruit, in order to accommodate very high levels of liquid humectant as a topical application, for infusion during a period of time in which the raisins are standing, e.g. during storage or shipment. These means include mechanical means, such as tumbling, or alternatively, ingredient means, such as the use of humectants containing thickeners.

This is a divisional of copending application Ser. No. 07/178,137 filedon 4/6/88 now U.S. Pat. No. 4,917,910.

BACKGROUND OF THE INVENTION It is nutritionally and organolepticallydesirable to provide fruits and fruit pieces in packaged dry foodproducts such as cookie mixes, muffin mixes, pancake mixes, cereal bars,and packaged ready-to-eat cereals, for example. However, such products,and typically ready-to-eat cereal products, being dry and havingrelatively low water activities, naturally tend to further desiccate thedry fruit. Hence, after a short time, untreated dried fruit, forexample, dried apples, bananas, currants, dates, peaches, prunes, etc.and of course, raisins, and mixtures thereof, tend to becomeunacceptably hard, or at least to become quite tough when packaged inthe presence of such dry products. Use of edible humectants such asglycerol to maintain the dried fruit in a softer, more desirablecondition, has been widely reported. Over 50 years ago, for example,John B. Segur et. al. received U.S. Pat. No. 1,853,151 which related tothe topical application of glycerine to raisins. The Segur Patenttaught, for example:

"Drying out of the fruits will occur and renders them harder andtougher.(Col. 1, lines 16-18.)

"In the preferred embodiment of the invention, a coating of glycerol isapplied superficially to the fruit which has been prepared for marketingin the usual manner and by common practices. This application may beeffected by spraying the dried fruit with glycerol or an aqueoussolution containing glycerol, or by immersing the fruits in glycerol oran aqueous solution containing glycerol. The quantity of glycerolapplied may vary within wide limits, but for practical purposes willordinarily not exceed 2 or 3% of the weight of the fruit, and in generalwill exceed 0.25%. For example, the dried fruit (prunes, for example) insuitable perforated trays or wire baskets or on a belt or perforatedconveyor, is sprayed with about 0.75% of its weight of 95% glycerol, toproduce a substantially uniform coating of glycerol thereon. (See column2, lines 66-86.) (Emphasis added.)

The Segur Patent goes on to teach:

Spray application is ordinarily desirable because of its readyadaptability to either manual or mechanical operation. If desired,however, the dried fruit may be immersed in glycerol . . . Prolongedimmersion is not required, as only superficial wetting of the surfacesof the fruit is desired. Thus, when the fruits are coated by immersion,it is ordinarily sufficient to immerse them (in perforated containers orwire baskets) in the liquid and immediately remove them. (Column 2, line96. to col. 3, line 9) (". . . " indicates a portion omitted.)

Immersing fruit such as raisins in glycerol as a means of both dryingand infusing the fruit with such a humectant is also disclosed in anumber of other patents and literature articles, such as the following.

U.S. Pat. No. 2,283,302, which issued in 1942 to W. A. Webb, teachesimmersing raisins in an edible liquid such as glycerine or otherspecified liquids. In a preferred process, the Webb patent teaches thepartial dehydration of the fruit, and subsequent impregnation withliquid glycerine, while it is immersed in the heated glycerine medium.The Webb Patent goes on to teach:

"The termination of the last stage of dehydration may, on the otherhand, be characterized by the continued presence of the circulatingliquid about and over the food. In such a case, restoration of normalpressure serves to drive the liquid into the cells and pores of thefood. The result is the full cell impregnation of the food. (Col. 2,lines 31 to 38)

U.S. Pat. No. 3,952,112, which issued in 1976 to C. V. Fulger et al.(and for which reexamination certificate B1 3,952,112 issued on Oct. 8,1985) also relates to the immersion i.e. static soaking of raisins inglycerine. Mr. Fulger also received U.S. Pat. No. 4,130,035 whichrelates to pretreating the raisins with alkali or hot weak acid toenhance the penetration of the glycerol.

U.S. Pat. No. 4,696,824, which issued on Sept. 29, 1987 to Meczkowski etal. also teaches coating raisins with glycerine followed by a coating ofoil.

Numerous other patents relate to the application of coatings of manykinds to serve as a moisture barrier for the raisins.

One of the major undesirable aspects associated with the immersion ofraisins in glycerol, is the fact that the raisin-skin transportphenomena is a two way street. The glycerol in which the raisins isimmersed soon becomes diluted with components which come out from theraisins. Sugars, water, and other components are the principle diluents.Some food processors regard the resulting diluted glycerol solution ofsuch components as being of sufficiently changed composition as to beunsuitable for extended immersion or repeated immersion of raisins, andthe resulting decanted liquid glycerol solution becomes a disposalproblem. This is not only a problem from the economic perspective, inview of all the wasted glycerol, but is also a problem from theenvironmental perspective, inasmuch as the waste material has a highbiological oxygen demand (BOD).

Hence, it has long been understood that for the purpose of admixing itwith a dry food, such as ready-to-eat cereal, for example, whichinherently has a relatively low Water Activity, fruit could bepretreated to provide internal humectant to maintain its softness.However, the prior art has not appreciated just how high the internalhumectant levels have to be in raisins, for example, in order tomaintain good properties in prolonged sealed storage, especially incereals having very low Water Activities, e.g. 0.3 or less, especially0.2 or less.

We have recently discovered that in prolonged storage in ready to eatcereals having very low Water Activities, e.g. 0.3 or less, the level ofglycerol infused into the raisins, for example, should be above about15% by weight, based on the weight of the glycerol infused product, inorder for the product to maintain its softness after storage in acontainer. This is vastly higher than the levels reported previously inthe literature, to our knowledge.

On the other hand, we have discovered that the maximum amount ofglycerol which can be applied to the surface of raisins, under simpletopical application procedure, such as be spraying, or immersing inexcess humectant and then removing the raisins from the glycerol, isabout 13.8%. This falls short of the minimum amounts believed necessaryto maintain softness in prolonged storage, in very low Water Activitydry food products, such as very low Water Activity ready-to-eat cereals.

It would be highly desirable to provide a process for manufacturingfruit having high levels of infused humectant such as glycerol, whichprocess does not inherently result in the generation of a waste glycerolstream.

It would be highly desirable to provide the art with a procedure forinfusing glycerol into raisins to result in internal levels of 14% ormore, which procedure utilizes only topical or surface application ofthe glycerol

It would also be highly desirable to provide dry food products such asready to use mixes, and ready-to-eat cereals, preferably ready-to-eatcereals having a very low Water Activity (e.g. 0.3 or less ), havingfruits such as raisins which do not become hard or tough on normalstorage in the food package.

THE DRAWINGS

FIG. 1 is a diagram setting forth the Water Activities of raisinstreated in accordance with the present invention, and of illustrativeready to eat cereal products. It also sets forth the range of preferredglycerol levels in the raisins intended for use in dry foods ofparticular Water Activity levels, in accordance with this invention.

FIG. 2 is also a diagram, identical to FIG. 1, but including indicia toillustrate the use of the diagram in selecting modes of practice, orembodiments, of the present invention, which are regarded by theinventors to be particularly suitable for different types of dry foods,such as mixes, and ready to eat cereals, for example, depending on theWater Activity of the dry food composition. FIG. 2 illustrates the useof FIG. 1 in connection with a dry food having an A_(w) of 0.10.

FIG. 3 is a diagram, very similar to FIG. 2, illustrating the use ofFIG. 1 in connection with the use of the present invention with dryfoods having low Water Activity levels e.g. about 0.35.

SUMMARY OF THE INVENTION

The objects referred to above, and other objects which will be apparenthereinafter, are all achieved in accordance with the present invention.

In its broadest aspects, the present invention involves applying arelatively high percentage of a liquid humectant to the surface of driedfruit, such as dried apples, bananas, currants, dates, peaches, prunes,etc. and of course, raisins, and mixtures thereof, and allowing the thuscoated fruit to stand for a period of time sufficient for the liquidhumectant to become infused into the fruit. More preferably, the liquidhumectant coated fruit is allowed to stand for a period of timesufficient for the liquid humectant to reach equilibrium with, and in,the fruit. And then the resulting liquid humectant infused fruit isadmixed with a dry food product, such as, for example a cookie mix, amuffin mix, a pancake mix, a cereal bar, a ready-to-eat cereal, or withcereal products, generally, and the resulting admixture is packaged intoa moisture barrier container. Hence, in accordance with a preferredembodiment of the present invention, raisins having humectant infusedtherein in amount of from about 7-14%, preferably from 10-14% areeminently satisfactory for use in dry foods such as mixes and ready toeat cereals having relatively low, but not extremely low, WaterActivity.

It has been noted, however, that it has been considered impossible toprovide very high levels of liquid humectant as a surface coating forfruits such as raisins, for example, by simple topical application, i.e.in amounts in excess of about 13-14% by weight, based on the weight ofthe mixture. Amounts in excess of those amounts would drain off theraisins. When the excess levels of humectant drain off, upon standing,the remaining raisins may be interacting with an inadequate quantity ofliquid humectant to achieve the humectant infusion levels one may desirein order to meet the objectives of softness, and in-storage stability ofthe softness, in a particular packaged environment with a dry food suchas a ready-to-eat cereal having a particular water activity.

We have discovered that special provision can made to increase thesurface carrying capacity of the fruit, such as raisins, for example.

These special means, in accordance with the preferred aspects of thepresent invention, can involve either mechanical processing means, oringredient means.

With respect to mechanical processing means, for example, we havediscovered that tumbling raisins in a bed of raisins will increase theliquid humectant surface-carrying characteristics of the raisins sothat, for example, raisins which would only hold about 13-14% glycerolon the surface, can carry, after tumbling, about 15-20% glycerol on thesurface with substantially no drainage of the glycerol from the raisins.The levels of applied glycerol which can be carried by the raisins aftercontinued tumbling for at least a half hour, or more, is well above thesum of the maximum amount carried on the surface without tumbling, plusthe amount infused into the raisins at the end of tumbling. We have noexplanation for this phenomenum.

Alternatively, ingredient means may be used to increase the levels ofliquid humectant which can be carried topically on the surface of thefruit, without substantial drain-off. For example, application of amixture of glycerol and a glycerol-thickening ingredient such assorbitol, to the surface of raisins, allows the deposition of levels ofhumectant in substantial excess of 13-14% on the surface, such as, forexample, levels of 15-20%, or higher.

Hence, in accordance with preferred aspects of the present invention, toprepare raisins for use in the presence of very dry foods, e.g. thosehaving a Water Activity of 3.0 or less, the thus surface-coated,glycerol-carrying raisins are allowed to stand e.g. are allowed toabsorb the humectant while in a relatively static condition, for aperiod of time sufficient for most of the surface humectant to infuseinto the interior of the raisins to an amount of at least about 15%glycerol. The thus infused raisins are then admixed with a dry food,such as those referred to earlier, for packaging in sealed moisturebarrier containers. The result is the successful maintenance of theperceivable "soft" character of the raisins during the usual storagetime which such products encounter until the product is consumed by theultimate user, i.e. during the "shelf life" of the product.

In accordance with the practice of the present invention, no wasteglycerol stream is ever generated, and yet very high levels of glycerolcan be infused into the interior of the raisins. The thus infused fruitscan be used to manufacture fruited dry food products, such as mixes andready to eat cereals, for example, even though the dry food product mayhave a very low water activity, e.g. 0.3 or less.

Admixing of ready-to-eat cereal and raisins with high levels oftopically applied glycerol still remaining on the surface of the raisinsresults in the absorption of the surface glycerol by the ready-to-eatcereal, instead of by the raisins. This would result in an inadequateamount of humectant to provide the desired level of infusion into theraisins. Hence, the utilization of the sequence of steps set forthherein, namely, the topical application of relatively high levels ofhumectant, the standing, and finally, the mixing of the resultingraisins with a dry food product, is critical to the optimum success ofthe process of manufacturing such a dry food product, in accordance withthis invention.

DESCRIPTION OF PREFERRED EMBODIMENTS

In a preferred embodiment of the present invention, at least about 10%glycerol is applied in the initial application of humectant to theraisins. The amount of glycerol which is added is preferably less thanthe amount which would create a pool of free liquid, or which wouldprovide sufficient glycerol to drain from the bed of raisins, e.g.between about 10% and 13% glycerol, based on the weight of the mixture,or with the special means referred to above, above 13%, e.g. between14-20%, inclusive.

Spraying onto a tumbling bed is the preferred method of achievingtopical application of liquid edible humectant. The spraying preferablytakes place on a mass or bed of raisins being tumbled. Although thetemperature of application is not critical, and can be made with theraisins and/or the liquid humectant either at ambient temperature, or atelevated temperatures, for example, higher rates of humectant infusionare noted at elevated temperatures.

The resulting raisins are then discharged from the tumbling device, andare preferably allowed to stand in a more or less static condition for asufficient time for most of the surface glycerol to be absorbed into theinterior of the raisins.

Without any special provisions, typically, depending on the size andother characteristics of the raisins, amounts up to about 13-14%humectant, preferably amounts between 10% and 13%, can be added to theraisins in a rotating tumbler without evidence of excess glycerol overthat required for mere topical application. In accordance with oneembodiment of the present invention, the ability or capacity of theraisins to carry higher amounts of surface glycerol is greatly increasedby continuing the tumbling action. Hence, even higher levels ofhumectant, such as glycerol, can be applied, for example, by modifyingthe tumbling conditions such as by repeating the spraying and tumbling,or by increasing the temperature, or by increasing the tumbling time. Inthe subsequent applications, incremental amounts of additional humectantwhich will not create pooling of humectant in the bed, for example,generally up to about 4% glycerol are added between tumbling cycles,until about 20-21% glycerol has been applied to the bed of raisins, forexample.

When it is desired to practice the present invention for the purpose ofproviding fruit for use in very dry food products, such as those havinga Water Activity of 0.3 or less, those embodiments which result inobtaining very high levels of glycerol infusion, e.g. above about 14%glycerol, based on the weight of the infused raisins, are preferred.Hence, such an embodiment involving repeating the sequence of steps oftopical application of liquid humectant, followed by tumbling, asdescribed immediately above, is a preferred method for such purposes.The quantity of glycerol which is added in each incremental addition ispreferably less than the amount which would provide a surface excess,i.e. less than the amount which would provide pools of free liquidwithin the bed, or which would provide sufficient amount to causesignificant liquid drainage from the bed.

In accordance with another preferred embodiment of the presentinvention, glycerol is sprayed on a tumbling bed of raisins, in onestep, in an amount sufficient to provide about 20% glycerol, based onthe weight of the resulting mixture, and the resulting mass is tumbledfor about 1-2 hours. Upon discharge, the glycerol is held on the surfaceof the raisins, and no drainage occurs. After several weeks to a monthof standing, the raisins are found to be infused with high levels ofliquid humectant. The liquid humectant-infused raisins are admixed, inaccordance with the present invention, with a dry food, such as a readyto use mix or a ready-to-eat cereal, and packaged in a sealed container.

Hence, alternatively, the entire final amount of liquid humectant, e.g.glycerol, can be added to the tumbling bed of raisins, and the tumblingcontinued until the liquid humectant carrying capacity is increasedsufficiently for the liquid humectant to remain as a topical applicationwithout drainage from the raisins in the bed.

With respect to the use of edible ingredient-means for increasing theamount of humectant carried on the surface of the raisins, preferrededible ingredients are those which will increase the viscosity of theprimary liquid humectant, without adversely affecting the handlingcharacteristics of the raisins. Examples of ingredients which actaccordingly, are edible gums, commercial water soluble dry matter suchas sucrose, glucose, sorbitol, and the like, or mixtures thereof. Theseingredients can be used in an amount of from

about 1-50% of the glycerol-thickener ingredient mixture, for example,as determined to be appropriate by simple experiment. It is noted thatfructose is a particularly undesirable glycerol thickening ingredient,since, during the tumbling, it soon results in a very sticky,unmanageable mass tending to adhere to the tumbler or conveyingequipment to the point of rendering it unusable. Whether an ediblematerial, known to be soluble in or with a liquid humectant is asuitable thickener, in accordance with this invention, is easilydetermined by a simple test of applying a mixture of that ediblematerial and the humectant to a small tumbling bed of raisins, andobserving whether the smooth rolling, tumbling action of the bed isencountered.

In a particularly preferred high temperature embodiment, the coating andtumbling steps are conducted at elevated temperature, e.g. at about 115degrees F. Sufficient glycerol is applied to provide about 13% glycerol,followed by an hour of tumbling, and then the sequence of glycerolapplication, followed by tumbling, is repeated twice, with about 4%glycerol being applied in each of the additional increments. In thisparticularly preferred embodiment, up to 6-7% glycerol can be diffusedinto the raisins, within twelve hours of tumbling. Upon standing, theraisins absorb almost all of the rest of the topically applied glycerol,to provide raisins with internal glycerol levels in the range of 15-18%.The standing step is employed to permit the absorption and uniformdiffusion of the glycerol within the fruit before the resulting fruit isadmixed with a dry food such as a ready-to-eat cereal.

DISCUSSION OF THE DRAWINGS

FIG. 1 is a diagram in which Water Activity, A₂, is plotted against"%Glycerol Infused Into Raisins." The single line represents the WaterActivity, A_(w), of raisins made in accordance with this invention. Thearea between the double parallel lines represents the preferred rangesof "%Glycerol Infused Into Raisins," for the respective dry foods havingthe specified Water Activities. At the right side of FIG. 1 is a secondvertical axis along which are listed representative Dry Foods, and theseitems are positioned at the Water Activity intersect representing atypical Water Activity for the item listed.

FIG. 2 is substantially identical to FIG. 1, except that indicia areprovided in FIG. 2 in order to illustrate the use of FIG. 1 indetermining preferred ranges of "%Glycerol Infused Into Raisins" forraisins intended for use in specific dry foods, e.g. ones havingspecific Water Activities. It also illustrates the use of FIG. 1 forcomparing the Water Activity of the raisins having the stated "%GlycerolInfused Into Raisins" with the Water Activity of the dry foods for whichit is preferred.

Referring now to FIG. 2, one may enter the diagram from either verticalaxis, for example at points A1 or A1'. Note that the exemplary A pointsrelate to a dry food product having a Water Activity of 0.1.

Hence, with respect to the A points, it is seen from FIG. 2 that thehorizontal line from points A1-A1', intersect the parallel obliquepreferred "%Glycerol Infused Into Raisins" lines to encompass a range offrom about 15-20% infused glycerol, the middle point A2 representingabout 17.5% "%Glycerol Infused Into Raisins" (See A3). Proceedingupwardly from the middle A2 value point, a vertical line intersects theWater Activity Raisin line at the horizontal line at A4. This intersectrepresents the Water Activity of the raisins with the "%Glycerol InfusedInto Raisins" level stated at A3.

In the illustration of FIG. 2, a ready to eat cereal having an A_(w) of0.1, would preferably utilize raisins having between 15 and 20% infusedglycerol in the raisins. Such raisins would be expected to have andA_(w) of about 0.4.

FIG. 3 is substantially identical to FIG. 1, except that additionalindicia are also provided in FIG. 3 in order to further illustrate theuse of FIG. 1 in determining preferred ranges of "%Glycerol Infused IntoRaisins" for raisins intended for use in the respective dry food items.Like FIG. 2, it also illustrates the use of FIG. 1 for comparing theWater Activity of the raisins having the stated "%Glycerol Infused IntoRaisins" with the Water Activity of the dry foods for which it ispreferred.

Referring now to FIG. 3, one may enter the diagram from either verticalaxis, for example at points B1 or B1'.

Likewise, with respect to the B points in FIG. 3, it is seen that theexemplary B1--B1', line represents dry foods having a Water Activity of0.35, such as, for example, many ready to use dry mixes, and many readyto eat cereals. This line intersects the oblique preferred range linesat points representing the range 10-15% "%Glycerol Infused IntoRaisins". Going downwardly from the range's middle point B2, thevertical intersects the axis line at a point B3 representing about 12.5"%Glycerol Infused Into Raisins". Going upwardly from B2, the verticalline crosses the Water Activity Raisins line at a point B4 whichrepresents the Water Activity of the raisins having the "%GlycerolInfused Into Raisins" represented at point B3.

In the example illustrated by FIG. 3, it is clear that, for dry foodshaving a A_(w) of about 3.5, the preferred range of % glycerol infusedinto the raisins in accordance with this invention is between 10% and15%, inclusive, and that the Water Activity of raisins having infusedglycerol level corresponding to the middle of that range is about 0.45.

Hence, it is clear from the Figures, that the practice of the presentinvention does not involve balancing Water Activity levels of the fruitwith the dry food. Rather, it involves providing levels of humectantwhich maintain softness for the normal times of storage in commercialpractice (Shelf Life).

Moreover, the two illustrative exercises shown in FIG. 2 and FIG. 3,which are provided as an illustrative aid for one with ordinary skill inthe art in interpreting FIG. 1, serve themselves to illustrate thepractice of the invention in two classes of embodiments, that is: oneclass, which does not require special means for increasing the surfacehumectant carrying capacity of the fruit (e.g. the B points, see FIG.3); and another class of embodiments which do (the A points, see FIG.2). It is also noted, however, that the practice of embodiments in therange around the point B2 encompasses both the kind of embodiments whichdo, and which do not, require means for increasing the surface humectantcarrying capacity of the raisins.

It is also noted that the raisin A_(w) values set forth on the Figures,represent an average around which test values were obtained. Forexample, the untreated raisin A_(w) value is about 0.575, representingan average of values ranging from 0.55 to 0.60. Also, the raisinstreated with 21% of a 96% glycerol solution to provide and internalglycerol level of 17.5% glycerol, is reported to be 0.40. However, thisrepresents an average of values in the range of 0.38 to 0.43.

It is emphasized that the values represented in the Figures for the dryfoods represent A_(w), values obtained without fruit being present.

EXAMPLES

The process of the present invention is further illustrated with the aidof the following examples. All temperatures are expressed in degreesFahrenheit, and all percents are in percent by weight, based on theweight of the material being referred to, unless otherwise indicated.All reference to parts refer to parts by weight, unless otherwiseindicated.

It is noted that this invention is applicable to the manufacture offruited dry foods, generally, and in the following examples, one classof these dry foods, namely ready to eat cereals, are used to exemplifythe application of the invention to dry foods, generally.

Likewise, this invention is applicable to the manufacture of fruited dryfoods containing any of a variety of dried fruits, and in the followingexamples, one class of these dried fruits, namely raisins, are used toexemplify the application of the invention to the manufacture of driedfruits, generally, and to the manufacture of fruited dry foods,generally.

Using the simple procedures discussed in the "Discussion of TheDrawings" section, above, and referring again to FIG. 1 FIG. 2, and FIG.3, it is a simple matter to select which of the above preferredembodiments of the present invention are regarded as best applicable toparticular ready to eat cereals, depending on the Water Activity of thedry food, such as a mix or a ready to eat cereal. The drawings willassist in determining whether embodiments providing high infusion ofliquid humectant, e.g. 7-13%, or very high levels of infusion of liquidhumectant, e.g. above 13%, should be evaluated for use with theparticular dry food product, depending on Water Activity. A number ofeach of these types of embodiments are illustrated in the followingnumbered examples.

EXAMPLE 1

This example illustrates the use of a preferred single step coatingembodiment for making a ready-to-eat cereal containing raisins. Raisinsare placed into a conventional tumbler to form a bed of raisins. Thetumbler is cylindrical in shape and is of stainless steel construction,open at only one end for loading and discharge. The "horizontal" axis ofthe tumbler is tipped somewhat downwardly towards the closed end duringthe loading and "tumbling" operations, and is tipped downwardly towardsthe open end during the discharge step. The raisins used in this exampleare "Midget" sized uncoated Thompson seedless raisins having 13-15%moisture. In this example, the rate of addition of glycerol iscontrolled to limit the application to topical, or surface only, coatingof the raisins. That is, the amount of glycerol added at any one time,and the rate at which it is added, is enough to simply coat the surfacearea of the raisins without immersing any of the raisins in liquid, ifthe bed of raisins were standing still at that moment. During the entireprocess of this example, the tumbler is running at 20 rpm, with the roomtemperature being in the range of 65-70 Degrees F. The glycerolingredient being applied is preferably 96% glycerol, 4% water, althoughsubstantially pure, 99%, glycerol is also eminently satisfactory.

In this example, glycerol is sprayed upon the bed of raisins at theratio of 21 pounds of glycerol per every 100 pounds of raisins. Thisquantity of glycerol is sprayed at a uniform rate over a 5 minute periodusing a standard, conventional "Flatjet" nozzle (TM Spraying Systems Co.of Wheaton, Ill.), and results in a raisin bed containing about 16.6%glycerol, and about 12.2-13.9% moisture. Tumbling is continued for about2 hours. After discharge from the tumbler, and upon standing, noglycerol drains from the raisins, and the absorption of the glycerolinto the raisins continues while the raisins are maintained in thestatic state.

After four weeks of standing, the resulting raisins are found to have aninternal glycerol content of about 15%. They are then admixed with aready-to-eat cereal having an A_(w) of about 0.20, in an amountsufficient to provide about 12% raisins in the resulting admixture, andthe resulting admixture is placed in a sealed moisture barrier package.As a test of shelf life storage stability, the resultingfruit-containing cereal is held in "accelerated storage conditions"(100-Degrees F. for two weeks) to simulate the results which wouldprevail when the product is stored for 6 months. At that time, thequality of the fruit is found to be vastly superior with respect tosoftness, when compared to the quality of untreated fruit, stored forthe same period of time, as a control, in the same ready-to-eat cereal.

EXAMPLE 2

This example is intended to illustrate a preferred multiple stepapplication of glycerol for infusion of very high levels of 91gycerolinto raisins in accordance with the present invention. The spraying andtumbling procedure of Example 1 is repeated. However, instead of asingle application of glycerol, 15.6 pounds of 96% glycerol is appliedper 100 pounds of raisins by spraying for 5 minutes onto the tumblingbed and continuing the tumbling for 1 hour. Without stopping thetumbler, another 5.45 pounds of 96% glycerol is added per 100 pounds ofinitial raisin charge. Each of the incremental additions of this exampleare made over a period of 5 minutes. Tumbling is continued for another25 minutes (providing a total lapsed time of 90 minutes). Anotherincremental addition of 96% glycerol is made in the amount of 5.45pounds per 100 pounds of initial raisin charge, and tumbling iscontinued for another 25 minutes. (About two hours lapsed since thefirst addition of 96 % glycerol.)

At this point the raisin bed in the tumbler comprises 20% totalglycerol, based on the weight of the mixture, and has 11.1-12.7%moisture on the same basis. Upon discharge from the tumbler, the raisinbed will not drip liquid if placed on a strainer or perforated tray.Upon standing in static condition for about 4 weeks, the internalglycerol content of the raisins is about 16%.

(See Example 4, below, for an illustration of the declumping of fruitproducts made in Example 2, for accurate metering for use of theresulting ingredient in a ready to eat cereal.)

EXAMPLE 3

The purpose of this example is to illustrate a variety of two and threestep sequence additions of glycerol to raisins in accordance withpreferred modes of the present invention.

The method of Example 2 is repeated in a number of tests, except thatthe amounts of glycerol added at each application differs according tothe amounts set out in Table 1, below. Hence, the first sprayapplication took place within the first 5 minutes of tumbling, andtumbling continued. A second spray application also took place after 1hour total tumbling time. The third spray application, if any, tookplace after 1.5 hours of total tumbling time, and a final 0.5 hours offinishing tumbling took place to provide a total of 2.0 hours oftumbling in each test. Fruit is not immersed in excess humectant at anytime during the tests.

                  TABLE 1    ______________________________________    % Topically Applied Glycerol Solution           1st        2nd         3rd    Test   Application                      Application Application                                          Total    ______________________________________    1      13.0       4.0         4.0     21.0    2      13.0       8.0         0.0     21.0    3      10.0       5.5         5.5     21.0    4      10.0       11.0        0.0     21.0    5      7.0        7.0         7.0     21.0    6      7.0        14.0        0.0     21.0    7      4.0        8.5         8.5     21.0    8      4.0        17.0        0.0     21.0    Range: 4.0-13.0   4.0-17.0    0-8.5   21.0    ______________________________________

In each of the above tests in accordance with the invention, theglycerol-carrying capacity of the raisins was high enough to result in aglycerol-coated raisin mixture which did not have excess, i.e.drainable, glycerol. The absence of "excess" can be determined by theabsence of free pools of liquid glycerol, when viewed thru the wall of aglass container, or by the absence of draining of glycerol from theraisins when placed on a screen, for example. The thus-coated raisins,after sufficient standing time to allow the penetration and uniformdiffusion of the glycerol into the raisins, are eminently satisfactoryfor use in accordance with the present invention for mixing with readyto eat cereals, for packaging and storage. The consumer perceives suchproduct mixtures as containing soft, moist fruit.

EXAMPLE 4

As indicated above, the raisin-skin transport phenomena involves a twoway diffusion, and some sugars, etc. come from within the raisins to thesurface, while the surface humectant migrates to the interior. Hence,after the time of standing, the raisins produced in accordance with thisinvention tend to "clump" together. The present example teaches a methodof "declumping" the resulting raisins on a large scale in connectionwith the subsequent metering of the raisins in the manufacture of aready-to-eat cereal.

In the manufacture of ready-to-eat cereal there is usually a stream of"fines" to contend with. These "fines" are merely bits and fragments ofthe bite-sized ready-to-eat cereal, as well as powdered cereal material.The purpose of this example is to illustrate the use of the fines toassist in the declumping and metering of the raisins produced inaccordance with the previous Example 2, after standing, and/orequilibrium.

The raisins produced in Example 2, after standing, are dumped into a pinmixer which consists of three rotating shafts with intermeshing pins.The rotation of the shafts causes the large clumps of raisins to breakup. The raisins are then discharged into Forberg (TM Clark ProcessingEquipment of Clarendon Hills, Illinois.) mixer. Here, 25 pounds ofready-to-eat cereal fines are added for every 75 pounds of treatedraisins. After mixing, the treated raisin/fines mixture is screened thrua two deck screener with a 1/2 inch RPT top screen and a 7 mesh bottomscreen. The top screen removes some of the raisins which may be stillclumped together, and the removed clumps are recycled thru the pinmixer. The bottom screen removes excess fines which are also recycledback to the Forberg Mixer. The resulting declumped raisins are now veryflowable, and can be metered accurately into a conventional ready-to-eatcereal packaging line with conventional belt feeders.

Ready-to-eat cereal having an A_(w) of 0.10 was admixed with thedeclumped raisins of this example in a ratio sufficient to provide anadmixture having about 10% raisins, to provide a fruited cereal withoutstanding quality fruit, even after 6 months of storage.

EXAMPLE 5

This example is provided to illustrate the bulk, one step addition ofglycerol to the tumbler at elevated temperatures. Nonetheless, it isnoted that the quantity of glycerol added, is less than that which willprovide excess liquid glycerol after the end of the tumbling cycle.Heated (115 degrees F), uncoated Midget sized Thompson seedless raisinsare placed into the tumbler described in Example 1, above. The moisturecontent of the raisins is also 13-15%. For every 100 pounds of raisins,26.5 pounds of 96% glycerol (4% water) is added to the bed. Heatedglycerol (115 Degrees F) is simply applied to the tumbling bed of fruit,as the tumbler rotates. The batch is tumbled for two hours at 20 RPM.After the tumbling cycle, the raisins appear to be moist, but no excessglycerol results. At this point, the overall composition of theraisin/glycerol bed is 20% glycerol, and between 11.1% and 12.7% water,depending on the initial moisture.

The glycerol content of the interior of the raisins at this point is5-6%.

After being discharged from the tumbler, and standing for 4 weeks, theinternal glycerol content of the raisins is 17%. The resulting raisinsmay be declumped as illustrated in Example 4, above. They are added to aready to eat cereal having A_(w) of 0.1, in an amount sufficient toprovide about 11% raisins in the admixture, and the resulting admixtureis packaged as a ready-to-eat cereal in a large scale production line.Again, after commercially prevailing periods of storage in the packagedready-to-eat cereal, the raisins of this example remain soft and have aneminently satisfactory flavor and consumer reaction.

EXAMPLE 6

The purpose of this example is to illustrate the effect of the tumblingat room temperature on the rate of infusion of glycerol into theraisins. In each of the following tests, a total of 21% of glycerol wasapplied to the raisin bed by spraying during tumbling. In Test A, nofurther tumbling was employed. In Test B, 2 hours of tumbling wasemployed. In Test C, the glycerol is added in increments; first, 13%,then after 1 hour tumbling, an additional 4%, and after 1.5 hours oftotal tumbling, a final 4% of glycerol is added. Tumbling is continuedfor a total of 2 hours before discharge from the tumbler. The tests wereconducted with 96% glycerol, and 99.5% glycerol, and the results weresubstantially comparable. Consequently only the results of the testsusing 96% glycerol are set forth below in Table 2.

                  TABLE 2    ______________________________________                     Internal Glycerol Content    Test and           0 Hr.    24 Hr.  7 Day    Conditions         Stand    Stand   Stand    ______________________________________    A.   Single spray/no Tumble                           0.5%     1.4%  5.3%    B.   Single Spray/2 Hr. Tumble                           0.9      2.8   6.9    C.   Serial spray/2 Hr. Tumble                           0.7      1.9   --    ______________________________________

Hence, in addition to increasing the glycerol-carrying capacity of theraisins, the tumbling has another positive effect, namely, it increasesthe speed of initial infusion of glycerol into the raisins.

DISCUSSION

The process of the present invention provides high levels of infusion ofhumectants such as glycerol into dried fruit in a process which does notgenerate a contaminated by-product humectant stream. The ready-to-eatcereals, to which the raisins produced in accordance with this inventionhave been added, remain soft and pleasing, thruout the shelf life of thefinished fruit-cereal mixture.

Any amounts of glycerol can be admixed with the dried fruit inaccordance the invention, from 10% upward, preferrably in the range of10-22%, using procedures such as those described herein, and in thepreceeding examples.

When the terms "dried fruit", or "fruit" are used herein, they areintended to include fruit generally, for example, dried apples, bananas,currants, dates, peaches, prunes, etc. and of course, raisins, andmixtures thereof.

The amount of fruit which is admixed with the dry food, in accordancewith this invention, is not critical, and is mainly a matter of taste.For example, amounts of fruit between about 5% and 30%, based on theweight of the treated fruit and dry food mixture, are eminentlysatisfactory. The use of raisins in ready-to-eat cereals in amountsbetween 7% and 15% are preferred, but substantially higher amounts canbe used, if desired.

Any commercially available raisins can be used in the process of thepresent invention. Preferred raisins are those having moisture levels inthe range of 13-15%.

The size of the raisins is not critical, and, for example, the so-calledMidget size, and the so-called Select size raisins are eminentlysatisfactory for use in accordance with the process of the presentinvention.

When the word "tumbling" is used herein, it refers to the actionencountered by a raisin in a bed of dried fruit, such as raisins in aconventional "tumbler," for example, in a rotatable drum which isrotatable around a generally horizontally aligned axis. Any mixer havinga similar configuration can be used as a tumbler in practicing themethod of this invention. Hence, "tumbling" the raisins, in accordancewith the process of the present invention, refers to the falling, androlling action provided by any mixer vessel which achieves mixing of itscontents mainly as a result of the rotation of the vessel about a moreor less horizontal axis.

A gentle rolling action of the bed is preferred, and although the use ofbaffles in the tumbler is acceptable, the use of powered stirrers shouldbe avoided. The tumbling operation uses conventional equipment which maybe either batch or continuous. In a continuous operation, fresh raisins,for example, enter an elongated revolving cylinder at one end thereof,and after proceeding in a tumbling, quasi-serpentine path thru thelength of the cylinder, are discharged at the other end. Both thebatch-type and continuous-type tumblers are well known, and conventionalenrobers are exemplary of highly satisfactory equipment for use astumblers in the method of the present invention.

When the liquid humectant, such as glycerol, is sprayed onto a tumblingbed of raisins, an amount of humectant which is near the maximum amountwhich can be topically applied, without the creation of pools ordrainable quantities of liquid humectant, is preferably sprayed upon thebed, and the resulting raisins are allowed to continue to tumble for aperiod of time, such as, for example, for a half hour to two hours.

The size or mass or depth of the beds of raisins which are tumbled inaccordance with the process of the present invention is not critical.However, the beds should not be so deep as to compress the raisins tosuch an extent that the raisins are reduced to a pulpy mass. We havefound that beds of raisins containing 500 pounds of raisins areeminently satisfactory for use in accordance with the present invention.

When sufficiently high levels of liquid humectant are topically applied,in accordance with this invention, liquid humectant levels well above10% are observed in the interior of the raisins within a few days ofstanding. In embodiments utilizing three incremental additions of liquidhumectant, for example, to provide surface liquid humectant levels of16-20%, internal liquid humectant levels of 15-18% are observed in theinterior of the raisins within several weeks. The resulting raisinsremain very soft, and are very stable in spite of storage within thearid, desiccating confinement of a very low A_(w) ready-to-eat cerealpackage.

It is preferred that the humectant be evenly, that is uniformly,distributed on the raisin surface, and this is preferably achieved byapplying the liquid humectant to the raisins during tumbling.

The rate or speed of application of the limited quantities of liquidhumectant to the raisins in the bed of the tumbler is not critical.However, it is preferred that the liquid humectant be sprayed upon thebed at such a rate as to simply topically apply the liquid humectant tothe raisins, and to create no masses or pools of excess free liquidhumectant within the bed. The temperature of the liquid humectant duringapplication is not critical, and can be at ambient temperature (70-75Degrees F.) or at elevated temperatures (e.g. at 115 deg. F., orhigher).

When the term "excess" of humectant or glycerol is used herein, it isintended to refer to quantities of humectant or glycerol which aregreater than the amount which will surface coat the raisins. Naturally,even the liquid-humectant or glycerol coated raisins which do not havean excess will tend to "wet" the walls of containers or screens, andsuch observations shouldn't be regarded as evidence of "excess."Drainage of a significant amount of humectant, such as glycerol, from abed would be regarded as evidence of an "excess."

When the term "liquid humectant"is used in connection with the practiceof the present invention, it is intended to refer to humectants whichare liquids at room temperature in their pure state. For example,glycerol and propylene glycol are eminently satisfactory for use inaccordance with the present invention as liquid humectants. However,this is not intended to infer that only pure humectant can be applied,in accordance with this invention. For example, concentrated aqueoussolutions of such humectants are eminently satisfactory for use inaccordance with this invention. It is clear that many examples areprovided herein in which 96% glycerol is used as the humectant, forexample.

On the other hand, humectants which are solids at room temperature intheir pure state, though they may be soluble in water to provide aqueous"humectant" solutions in conventional usage of the word, are notsuitable for use in the present invention. For example, application of asaturated aqueous pure sorbitol solution on the surface of raisins, upontumbling, almost immediately results in a white solid layer on theraisins. After standing, mixing with a ready to eat cereal, and storage,the resulting raisins are glassy. And rather than being soft, theyfracture along smooth planes, much as a glass sphere would, upon beingbitten-into. Nonetheless, sorbitol can be used as a liquid humectantthickener, as discussed above. In addition, vegetable gums which aresoluble in the particular humectant are also satisfactory thickeners, inaccordance with this aspect of this invention. Such gums can be used inthe liquid humectant at very low levels, for the purpose of thickeningthe liquid humectant.

When the words "stand" or "standing" are used herein, it is to beunderstood that the raisins need not be motionless, and that the"standing" step can take place while the product is being shipped, orotherwise moved about. The terms refer to a relatively static conditionof the fruit which allows the liquid humectant to diffuse from thesurface of the fruit thruout its interior. Hence, this condition canoccur while the fruit is in the one location, or in transit, and canlast for several hours or several weeks, depending on the method usedand the desired results.

When the word "packaging" is used herein, it is intended to refer to anykind of moisture barrier confinement, such as in the use of any of theconventional systems presently being used to package ready to eatcereal. It is also intended to include bulk moisture barrierconfinement, such as in drums, boxes, cartons, cans, bottles, tubes,bags, etc.

With respect to the use of the terms "Water Activity", or "A_(w) ", asused herein, these terms have their conventional meaning. The values forA_(w), or Water Activity, which are reported herein, are either takenfrom the public literature, such as patents, or are determined bylaboratory testing. The values reported herein which were the result oftesting, were determined using a Thermocouple Psychrometer SC10, (TMDecagon Devices, Pullman, Washington). This devise is used in connectionwith a 21X Micrologger (TM Campbell Scientific, Inc) for a digitalreadout. The intermittent, pulsed readings, at approximately one secondintervals, are plotted, and the low (equilibrium) reading is recordedand reported as the A_(w).

I claim:
 1. A process for infusing liquid humectant into dried fruit, comprising: applying a predetermined amount of liquid humectant topically to a bed of dried fruit pieces wherein the liquid humectant includes an edible thickener, the amount of liquid humectant applied to be at least about 20% of the weight of the resulting admixture of dried fruit pieces and liquid humectant but less than the amount which would produce pools of free liquid in the bed; and allowing the dried fruit and liquid humectant to stand until most of the liquid humectant has been infused into the dried fruit.
 2. The process of claim 1, wherein the liquid humectant is selected from the group consisting of glycerol and propylene glycol.
 3. The process of claim 1 wherein the dried fruit pieces are selected from the group consisting of apples, bananas, currants, dates, peaches, prunes, raisins and mixtures thereof.
 4. The process of claim 1 wherein the dried fruit pieces are raisins.
 5. The process of claim 1 wherein the amount of liquid humectant applied is at least about 13% of the weight of the resulting admixture of dried fruit pieces and liquid humectant.
 6. The process of claim 1 wherein the edible thickener is selected from the group consisting of edible gums, sucrose, glucose, and sorbitol.
 7. A process for infusing glycerol into raisins, comprising: applying a predetermined amount of glycerol topically onto a bed of raisins wherein the glycerol includes an edible thickener, the amount of glycerol applied to be at least about 10% of the weight of the resulting admixture of raisins and glycerol but less than the amount which would produce pools of free liquid in the bed; and allowing the raisins and glycerol to stand until most of the glycerol has been infused into the raisins.
 8. The process of claim 7 wherein the edible thickener is selected from the group consisting of edible gums, sucrose, glucose, sorbitol and mixtures thereof.
 9. The process of claim 7 wherein the amount of glycerol applied to the raisins is at least about 13% of the weight of the resulting admixture of raisins and glycerol.
 10. A process for manufacturing packaged, fruited dry food compositions comprising: applying a predetermined amount of liquid humectant topically to a bed of dried fruit pieces wherein the liquid humectant includes an edible thickener, the amount of liquid humectant applied to be at least about 10% of the weight of the resulting admixture of dried fruit pieces and liquid humectant but less than the amount which would produce pools of free liquid in the bed; allowing the dried fruit and liquid humectant to stand until most of the liquid humectant has been infused into the dried fruit; and admixing the resulting humectant-infused dried fruit with a dry food composition, and packaging the resulting fruit-containing dry food composition.
 11. The process of claim 10 wherein the liquid humectant is selected from the group consisting of glycerol and propylene glycol.
 12. The process of claim 10 wherein the dried fruit pieces are selected from the group consisting of apples, bananas, currants, dates, peaches, prunes, raisins and mixtures thereof.
 13. The process of claim 10 wherein the dried fruit pieces are raisins.
 14. The process of claim 10 wherein the edible thickener is selected from the group consisting of edible gums, sucrose, glucose, and sorbitol.
 15. The process of claim 10 wherein the liquid humectant is applied to the dried fruit by spraying.
 16. The process of claim 10 wherein the amount of liquid humectant applied is at least about 13% of the weight of the resulting admixture of dried fruit pieces and liquid humectant.
 17. The process of claim 10 also comprising the step of declumping the humectant-infused dried fruit pieces by agitating them in the presence of cereal fines.
 18. The process of claim 10 wherein the dry food composition has a water activity below about 0.3 and the dried fruit pieces have a water activity of about 0.4.
 19. A process for manufacturing packaged, raisin containing ready to eat cereal compositions comprising: spraying a predetermined amount of glycerol topically onto a bed of raisins wherein the glycerol includes an edible thickener, the amount of glycerol sprayed to be at least about 10% of the weight of the resulting admixture of raisins and glycerol but less than the amount which would produce pools of free liquid in the bed; allowing the raisins and glycerol to stand until the raisins have achieved a water activity of about 0.4; admixing the resulting glycerol-infused raisins with a ready to eat cereal composition having a water activity below about 0.3; and packaging the resulting raisin-containing ready to eat cereal composition.
 20. The process of claim 19 wherein the edible thickener is selected from the group consisting of edible gums, sucrose, glucose, and sorbitol.
 21. The process of claim 19 wherein the amount of glycerol sprayed is at least about 13% of the weight of the resulting admixture of raisins and glycerol.
 22. The process of claim 19 also comprising the step of declumping the glycerol-infused raisins by agitating them in the presence of cereal fines. 